Portable electronic devices, such as smart phones, include a camera module. Due to the portable electronic devices becoming smaller, the camera module is actuated by a finger action on a touch screen of the portable electronic device, rather than a physical button arranged on the portable electronic device. However, it needs time to unlock the screen, start a camera application, and actuate the camera module by controlling the camera application. A best shooting chance may be missed when operating the steps above. Therefore, there is still improvement in the art that the camera module may be actuated faster by cooperating with other components of the portable electronic device, such as a casing.